How did the idea of Exception-handling emerge into programming languages? [duplicate]

Question

Possible Duplicate:
Who designed exceptions?

Today if we look at any language, exception handling is almost a compulsory feature. The languages that didn't have it earlier are implementing it in their later versions.

I wonder how this idea emerged, because exceptions have a totally separate flow running in parallel with the main code flow and can interrupt the main flow at any point.

IMHO the idea is a bit mind-bending. So, how did this idea surface? A bit of history?

Note to avoid closing(Not worked): And by History I did not mean the dates, times, names and places. I actually wanted to know the informal history that how the idea bubbled up into the languages. Did it came from any sort of programming best practices? Or it was someones idea at the first place?

Answer 1

The first language of which I'm aware that included exception handling was PL/I, in 1964¹.

It did give exception handling a bit of a bad name, as it used them to handle situations I doubt anybody would treat as exceptions in most modern languages (e.g., reaching the end of a file).

It was prompted largely by Fortran, which (in early versions) provided no way to detect such conditions (including detecting when you'd reached the end of a file).

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¹It was originally defined in 1964. Actual compilers came somewhat later, and the definition was still in flux until around 1967 or 1968.

Answer 2

THROW was in Lisp in the 70s, and longjmp was in C, paired with setjmp around the same time.

Added: You're asking how they got the idea.

OK, if you're coding away in any language, writing routines, calling routines, trying to figure out how to handle conditions you didn't expect, you have options like "set a global error variable and return", or "have an error return code that the caller has to check".

Inevitably you start strongly wishing "There's got to be a better way to do this. Couldn't I just blast out of here?" If you're doing any assembly language at all, you know in principle it's very simple.

That's how.

Answer 3

Well, it emerged as a debugging tool but soon made it's way into run-time implementation in languages like LISP and C.

There are however, multiple types of/ways to preform exception handling and it's all based on perspective.

You probably mean exception handling in the form of try-catch statements, however this is also a type of manual exception handling (C++), and it's been around forever:

    int* pA;
    pA = new int[20];
    if( pA == 0 )
       cout<<"Memory could not be allocated!"<<endl;